The present invention relates to a heat exchanger of the type having a heat exchange block comprising a plurality of tubes and fins extending transversely to the tubes, a synthetic resin tube plate receiving the tubes, and a synthetic resin water tank attached to the tube plate. The invention also concerns a process for manufacturing such a heat exchanger.
A tube/tube plate joint for round tubes of a heat exchanger is known from GB No. 1,445,598. The tube plate is made of metal and is equipped with passages into which the ends of the heat exchanger tubes are inserted. Subsequently, a pressure fit is established through radial expansion of the tube ends, whereby the tube ends are fastened and sealed in the tube plate.
This known process, because of the necessary material properties, is applicable only when metal tube plates are used. In the case of heat exchangers with metal tube plates, a water tank formed of synthetic plastic material can be connected to the tube plate only with mechanical connectors. Thus, a separate sealing element, usually in the form a rubber gasket, is required.
From DE-OS No. 21 25 671 a process for the production of radiators with tube plates consisting of a synthetic plastic material is known. In the process, the plastic material of the tube plates is gradually melted by the application of ultrasonic vibrations and simultaneously the tubes penetrate the plate under pressure. The joining of the water tank with the tube plate is again effected by the application of ultrasonic vibrations to the boundary layers in contact with each other, whereby they are gradually made to melt and are thus welded together.
In the ultrasonic welding method, the necessary welding heat is generated by boundary layer friction. Thus, the vibrations produced by this method must be perpendicular to the surface being welded. Difficulties with the introduction of the vibration often arise depending on the configuration of the parts to be joined together. Consequently, in ultrasonic welding, configuration guidelines concerning the shape of the parts and the position of the directional energy guides must be observed with high accuracy. Furthermore, in this method, tolerances must be kept extraordinarily small, so that satisfactory welding may occur at all. Actual practice has also shown that ultrasonic welding is practical only for small or medium sized parts. It is difficult furthermore to obtain the strength and tightness required of heat exchangers under pressure by the ultrasonic welding process.